Dire
hyenas (known to many as hyaenodons) are more fearsome than their
smaller cousins. While hyaenodons won't turn down carrion as a handy
meal, they much prefer to hunt for prey. A pack of dire hyenas rarely
stops moving and hunting for anything other than sleep, mating, or
food. Hyaenodons are 6 feet tall at the shoulder and often over 12 feet
long. They weigh 900 pounds.

Gnolls have been known to train hyaenodons to serve in their lairs as guardians, or more commonly as fearsome mounts.